Recently, the brilliant developments of vacuum technique give an impetus to the commercialization of various advanced technologies using vacuum. In particular, plasma processes show the remarkable growth and are extensively used in the manufacturing and processing of various materials throughout the whole industry.
Plasma polymerization is one of such plasma processes and is technique using the coating phenomenon of a polymer material produced during the conversion of gases and organic vapors to plasma at a low pressure to coat a solid surface with the polymer material as a thin film.
This phenomenon was found by chance during studying plasma using electrical discharge in 1950s, however did not attract attention for a long time, but attracts attention as a novel method for synthesizing a polymer after identifying that the material thus produced is a polymer material only until 2008.
Meanwhile, a polydopamine was firstly reported as an adhesive polymer imitating the adhesive mechanism of a mussel adhesive protein in 2007s. As the polydopamine is known to be coated on almost all organic materials, inorganic materials such as metals, ceramics, semiconductor materials, and synthetic polymers in an aqueous solution under oxidation conditions to form an active surface, the polydopamine receives attention in various technical fields. Since the material is imitated from mussels, the biocompatibility thereof is very good, and the material may be coated on almost all surfaces. Since the coated surface is active, a novel material may be introduced onto the polydopamine coating. In the case of applying the polydopamine to various synthetic polymers/natural polymers, the polymers also have adhesiveness and coating ability, and may be applied in various techniques.
For example, it is reported that cell cultivation may become possible by introducing the polydopamine coating on a surface to which cell cannot be attached such as polyethylene, silicon rubber and PDMS (S. H. Ku et al., Biomaterials 2010, 31, 2535). An adhesive chitosan hydrogel is formed by introducing polydopamine to chitosan which is a natural polymer and is actively studied as a polymer for medical use, and a hemostatic using the same was developed (J. H. Ryu et al., Biomacromolecules 2011, 12, 2653). Besides, the polydopamine is introduced to typical polymers for medical use, which includes hyaluronic acid, polyethylene glycol (PEG), etc. to develop an adhesive polymer for diversely applying the same in medical/bio fields for modifying a biocompatible surface, for forming hydrogel, etc.
In addition, application study on the polydopamine in an energy field also receives attention, and adhesiveness is imparted by introducing the polydopamine to a polymer such as arginic acid, and polyacrylic acid, which are used as the binder of a lithium ion battery, and the adhesiveness between a binder and an electrode may be improved, thereby significantly increasing the capacity and the life of the battery.
The polydopamine may be biosynthetically obtained from DOPA which is a material playing the core role in the function of the adhesive protein of a mussel. In FIG. 2, the biosynthetic process of such catecholamine is schematically illustrated.
“DOPA” is a precursor material produced during the biosynthesis of catecholamine, and tyrosine which is an amino acid is converted to L-DOPA in catechol series by tyrosine hydroxylase. DOPA is the abbreviation of 3,4-dihydroxy-L-phenylalamine and is also called as L-DOPA (levo DOPA or L-3,4-dihydroxyphenylalamine). A DOPA material may be purchased and used, and is generally purchased as a powder shape.
However, until now, the polydopamine is used as an aqueous solution of a commercially available DOPA powder or by the self polymerization of dopamine formed in a mixture solution of an aqueous solution and an organic solution, or may be extracted from an organism such as a mussel. However, the application of the polydopamine for the surface modification by dry plasma polymerization has not been reported. That is, the polydopamine has not been used through artificial synthesis via plasma polymerization.
The inventors of the present application found that a catecholamine compound such as polydopamine may be synthesized by using aniline, etc., as a starting material not by the conventional dip-coating method but by a dry plasma polymerization process, and the catecholamine thus synthesized has a uniform thin film shape and has effective surface modification effects at the same time, and completed the present invention.